To shore up support for Proposition 30, Gov. Jerry Brown goes on a 5-city swing to tout his proposal to raise taxes and head off deep cuts to public education.

Gov. Jerry Brown speaks at a rally in support of Proposition 30 held Monday… (Gary Friedman, Los Angeles…)

SACRAMENTO — Gov. Jerry Brown darted across the state Monday in a last-minute bid to shore up support for Proposition 30, his proposal to raise taxes and head off billions of dollars in cuts to public education.

The five-city swing, stretching from San Diego to San Francisco, underscored the precarious position of the governor's tax measure in the final hours of the campaign — and its importance to his governorship. Recent polls showed support for the proposal slipping below 50%, often the death knell for tax initiatives.

Early in the morning, standing before more than 100 students and teachers outside a San Diego high school, Brown struck a populist tone, emphasizing that people making more than $250,000 would pay most of the new levies.

"Do we want our schools to cut $6 billion more," Brown asked, "or do we ask those who have enjoyed the greatest benefits to give a little more to California in our time of need?"

Brown, who campaigned for office on a promise to repair California's finances, has redoubled his efforts in recent weeks to pass Proposition 30.

He spent the weekend in Los Angeles, rallying union workers at a canvassing drive, making calls with volunteers at a phone bank and taking the pulpit at four churches. Between events, the governor has encouraged his more than 1 million Twitter followers to vote and highlighted support from labor leaders, lawmakers — even Oakland native and '90s rapper MC Hammer.

Other high-profile initiatives, however, are competing for Californians' attention.

Millionaire civil rights lawyer Molly Munger has spent more than $47 million to promote a different tax measure, Proposition 38. It would increase income taxes on most Californians to raise an estimated $10 billion a year for schools and to pay down state debt.

Business and labor groups have bombarded voters with mail and television ads about Proposition 32, which would curb the political influence of unions in state politics. Polls show the measure languishing.

Proponents, including Republican donors, anti-tax activists and business executives, say Proposition 32 is an even-handed effort, eliminating the ability of corporations and unions to deduct political contributions from workers' paychecks. Labor leaders counter that payroll deductions are their main fundraising tool; businesses typically tap executive checkbooks and company treasuries.

Backers of a proposal to place special labels on genetically engineered food made a last-ditch effort to stem declining support. They poured millions of dollars into new ads for Proposition 37 after a monthlong barrage of critical spots from the opposition.

Biotechnology firms led by Monsanto Co. and Dow Chemical Co. argue that the measure is unnecessary and would raise food prices. Supporters say Californians deserve to know what's in their food.

Other proposals on the ballot include far-reaching criminal justice measures. Proposition 34 would abolish the death penalty. Proposition 36 would ease the state's tough "three strikes" sentencing law. Both campaigns are running TV ads.

State voters will also cast ballots in a U.S. Senate race, in which Democrat Dianne Feinstein is seeking reelection, and dozens of competitive congressional and legislative races that could give Democrats a supermajority in the state Senate and swell the party's numbers in Washington.

New political maps drawn by an independent commission rather than elected officials have created more competitive races than the state has seen in more than a decade. Outside groups have spent more than $53 million to influence congressional races and more than $20 million has been expended in contests for the Legislature.